The present invention is in a composite adhesive web and a process for its production.
British Pat. No. 1,117,751 describes the reproduction of a thermally adhesive web from a tissue of randomly arranged thermoplastic filaments. The webs are widely used in combination with nonwoven materials as stiffening interlinings, which can be ironed onto materials to be stiffened, i.e., garment parts.
In the method of the British Specification, thermoplastic material is continuously extruded and collected as a web on a continuously moving sheet. The moving sheet is preferably a nonwoven. The filaments in the web are caused or allowed to fuse to one another and to the sheet to form a fusible interlining for various apparel applications.
The thermoplastic polymers can be extruded and collected as a web on a continuously moving sheet, where the filaments are caused or allowed to fuse to one another, but not to the sheet. In this case, the tissue of the randomly arranged thermoplastic filaments bonded to one another can easily be removed from the carrying sheet to form a thermally adhesive web.
The extrusion process to form a web from randomly arranged thermoplastic filaments can be as described in British Pat. No. 1,117,751 or in a meltblown process as described in U.S. Pat. No. 3,825,380.
The webs of the prior art are useful as thermal adhesives in various textile interlining and other applications. The webs are lightweight typically weighing from 20 to 80 g/sq.m. Because the webs are thin and light, they have a rather low tensile strength. Heavier webs tend to be firm but brittle.
It is often desired to use the web in form of a tape. Typically the minimum width is 10-13 mm. However, because of the low tensile strength and/or brittleness, and because of the difficulties in handling the tape, especially using high speed mechanical handling apparatus, it is necessary to insure that the tape has sufficient tensile strength. If the tape does not have sufficient strength it will break during handling. Despite the above and other difficulties, thermally adhesive webs have been widely used and have gained recognition as important materials. However, the above-described disadvantages have imposed some constraints on their application.
A thermal adhesive web of improved tensile properties can be formed according to U.S. Pat. No. 4,490,427 which discloses a web wherein parallel filaments of thermally adhesive polymers are bonded to, and interconnected by, randomly arranged polymeric fibers. The use of parallel arranged thermoplastic filaments improves the tensile strength of such a material, but still not to the desired tensile strength.
U.S. Pat. No. 4,440,819 discloses multidirectional fiber arrays wherein graphite, glass or other fibers in substantially unidirectional arrays are interconnected with polymeric fibers. Interconnected material may subsequently be layered, impregnated with resin and laminated to yield unidirectional fibers/resins/polymer fiber composites.
However, it has been found that thermally adhesive webs of the prior art lack the desired tensile - elongation properties especially at weights over 40 g/sq.m.